A nuclear stress test measures blood flow to your heart at rest and while your heart is working harder as a result of exertion or medication. The test provides images that can show areas of low blood flow through the heart and damaged heart muscle.

The test usually involves taking two sets of images of your heart — one while you're at rest and another after you heart is stressed, either by exercise or medication.

You may be given a nuclear stress test, which involves injecting a radioactive dye into your bloodstream, if your doctor suspects you have coronary artery disease or if a routine stress test didn't pinpoint the cause of symptoms such as chest pain or shortness of breath. A nuclear stress test may also be used to guide your treatment if you've been diagnosed with a heart condition.

Your doctor may recommend a nuclear stress test to:

Diagnose coronary artery disease. Your coronary arteries are the major blood vessels that supply your heart with blood, oxygen and nutrients. Coronary artery disease develops when these arteries become damaged or diseased — usually due to a buildup of deposits called plaques.

If you have symptoms that might indicate coronary artery disease, such as shortness of breath or chest pains, a nuclear stress test can help determine if you have coronary artery disease.

See the size and shape of your heart. The images from a nuclear stress test can show your doctor if your heart is enlarged and can measure its pumping function (ejection fraction).

Guide treatment of heart disorders. If you've been diagnosed with coronary artery disease, arrhythmia or another heart condition, a nuclear stress test can help your doctor find out how well treatment is working. It may also be used to help establish the right treatment plan for you by determining how much exercise your heart can handle.

A nuclear stress test is generally safe, and complications are rare. But, as with any medical procedure, it does carry a risk of complications, including:

Allergic reaction. You could be allergic to the radioactive dye that's injected into a vein in your hand or arm during a nuclear stress test, but this is rare and reactions are usually mild.

Abnormal heart rhythms (arrhythmias). Arrhythmias brought on either by exertion or the medication used during a stress test usually go away shortly after you stop exercising or the medication wears off. Life-threatening arrhythmias are rare.

Flushing sensation or chest pain. These symptoms can occur when you are given a medication to stress your heart if you're unable to exercise adequately. These symptoms are usually brief, but tell your doctor if they occur.

You may be asked not to eat, drink or smoke for two hours before a nuclear stress test. Ask your doctor if you should avoid caffeine or certain medications the day before the test, because they can interfere with certain stress tests. Otherwise, you can take your medications as usual.

If you use an inhaler for asthma or other breathing problems, bring it to the test. Make sure your doctor and the health care team member monitoring your stress test know that you use an inhaler.

Wear or bring comfortable clothes and walking shoes.

A nuclear stress test can take two to five hours. When you arrive, you'll be asked about your medical history and how often and strenuously you exercise.

During a nuclear stress test

Before you start the test, a technician inserts an intravenous line (IV) into your arm or hand and places sticky patches (electrodes) on your chest, legs and arms, which connect by wires to an electrocardiogram machine. The electrocardiogram records the electrical signals that trigger your heartbeats. A cuff on your arm checks your blood pressure during the test.

If you're unable to exercise adequately, you may be given a medication through your IV that increases blood flow to your heart muscle — simulating what exercise does — for the test. Depending on which medication is used, possible side effects may be similar to those caused by exercise, such as a flushing or shortness of breath.

If you're exercising, you'll likely begin walking on the treadmill slowly. As the test progresses, the speed and incline of the treadmill increases. You can use the railing on the treadmill for balance, but don't hang on tightly, as this may skew the results of the test. On a stationary bike, the resistance increases as the test progresses, making it harder to pedal.

You continue exercising until your heart rate has reached a set target, you develop symptoms that don't allow you to continue or you develop:

Moderate to severe chest pain

Severe shortness of breath

Abnormally high or low blood pressure

An abnormal heart rhythm

Dizziness

You can stop the test any time you're too uncomfortable to continue.

Injection of dye

A radioactive dye is injected into your bloodstream through the IV. First, images will be taken of your heart at rest. Then, after you've exercised or been given medication to stimulate your heart, you'll receive more radioactive dye through the IV. You'll again lie on a table while a scanner similar to an X-ray machine creates images of your heart muscle. The dye shows inadequate blood flow to part of your heart as a light spot on the images.

The two sets of images allow your doctor to compare the blood flow through your heart while you're at rest and while your heart is pumping harder as a result of exercise or medication.

After a nuclear stress test

When the test is complete, you may return to normal activities unless your doctor tells you otherwise. The radioactive material will naturally leave your body in your urine or stool, but drinking plenty of water will help flush the dye out of your system.

Normal blood flow during exercise and rest. You may not need further tests.

Normal blood flow during rest, but not during exercise. Part of your heart isn't receiving enough blood when you're exerting yourself, which may indicate one or more blocked arteries (coronary artery disease).

Low blood flow during rest and exercise. Part of your heart isn't getting enough blood at all times, which could be due to severe coronary artery disease or previous heart attack.

Lack of radioactive dye in parts of your heart. Areas of your heart that don't show the radioactive dye have tissue damage from a heart attack.

If you don't have enough blood flow through your heart, you may need to undergo coronary angiography — a test to look directly at the blood vessels supplying your heart. If you have severe blockages, you may need a coronary intervention (balloon angioplasty and stent placement) or open-heart surgery (coronary artery bypass).

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